(Braak 1928) Werkman and Gillen 1932
Citrobacter freundii is a species of facultative anaerobic gram-negative bacteria of the family Enterobacteriaceae. The bacteria have a long rod shape with a typical length of 1–5 μm. Most C. freundii cells generally have several flagella used for locomotion, but some do not and are non-motile. C. freundii is a soil organism, but can also be found in water, sewage, food and in the intestinal tracts of animals and humans. The genus Citrobacter was discovered in 1932 by Werkman and Gillen. Cultures of C. freundii were isolated and identified in the same year from soil extracts.
C. freundii is a common component of the gut microbiome of healthy humans. While most strains are beneficial, there are significant phenotypic variations among strains, even those that share >99% of their genome. Some rare strains of C. freundii have been associated with opportunistic nosocomial infections of the respiratory tract, urinary tract, blood, and many other normally sterile sites in immunocompromised patients.
C. freundii is also commonly found to be a member of the soil microbiome. This microbe plays an important role in the nitrogen cycle in the environment. C. freundii is responsible for reducing nitrate to nitrite in the environment. This conversion is an important and crucial stage in the nitrogen cycle.
C. freundii has the ability to grow on glycerol, and use it as its sole source of carbon and energy. The organism contains a bacterial microcompartment which is capable of processing propanediol. C. freundii creates a positive MR and negative VP test along with a positive Catalase and negative Oxidase test. C. freundii cannot hydrolyze starch, lipids, or gelatin. 
- LPSN bacterio.net
- "Citrobacter SPP". Pathogen Safety Data Sheet — Infectious Substances. Public Health Agency of Canada. 2012.
- Wang, J. T.; Chang, S. C.; Chen, Y. C.; Luh, K. T. (2000). "Comparison of antimicrobial susceptibility of Citrobacter freundii isolates in two different time periods". Journal of Microbiology, Immunology, and Infection = Wei Mian Yu Gan Ran Za Zhi. 33 (4): 258–262. PMID 11269372.
- Schloissnig, Siegfried; Arumugam, Manimozhiyan; Sunagawa, Shinichi; Mitreva, Makedonka; Tap, Julien; Zhu, Ana; Waller, Alison; Mende, Daniel R.; Kultima, Jens Roat (2013-01-03). "Genomic variation landscape of the human gut microbiome". Nature. 493 (7430): 45–50. doi:10.1038/nature11711. ISSN 0028-0836. PMC 3536929. PMID 23222524.
- Morowitz, Michael J.; Denef, Vincent J.; Costello, Elizabeth K.; Thomas, Brian C.; Poroyko, Valeriy; Relman, David A.; Banfield, Jillian F. (2011-01-18). "Strain-resolved community genomic analysis of gut microbial colonization in a premature infant". Proceedings of the National Academy of Sciences. 108 (3): 1128–1133. doi:10.1073/pnas.1010992108. ISSN 0027-8424. PMC 3024690. PMID 21191099.
- Whalen, J. G.; Mully, T. W.; English, J. C. (2007). "Spontaneous Citrobacter freundii Infection in an Immunocompetent Patient". Archives of Dermatology. 143 (1): 124–125. doi:10.1001/archderm.143.1.124. PMID 17224563.
- Puchenkova, S. G. (1996). "Enterobacteria in areas of water along the Crimean coast". Mikrobiolohichnyi Zhurnal (Kiev, Ukraine : 1993). 58 (2): 3–7. PMID 8983520.
- Pang, A.; Warren, M. J.; Pickersgill, R. W. (2011). "Structure of PduT, a trimeric bacterial microcompartment protein with a 4Fe–4S cluster-binding site". Acta Crystallographica Section D. 67 (2): 91–96. doi:10.1107/S0907444910050201. PMID 21245529.
- "Citrobacter freundii". NCBI Taxonomy Browser. 546.
- Type strain of Citrobacter freundii at BacDive - the Bacterial Diversity Metadatabase
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